Epstein-Barr Virus-Positive Primary CNS Lymphoma in a Patient Receiving Mycophenolate Mofetil: Diagnostic and Therapeutic Considerations.

Epstein-Barr virus (EBV)-positive primary central nervous system lymphoma (PCNSL) is a rare entity typically associated with profound immunosuppression, most commonly in transplant recipients or individuals with HIV. We report a case of EBV-positive PCNSL arising in a 75-year-old male with myasthenia gravis receiving chronic mycophenolate mofetil (MMF) therapy outside the transplant setting. The patient presented with progressive neurological deficits, and brain magnetic resonance imaging demonstrated multiple enhancing lesions. Stereotactic biopsy revealed diffuse large B-cell lymphoma of non-germinal center subtype with immunoblastic features and EBV-encoded RNA (EBER) positivity, confirming EBV-positive PCNSL. MMF was discontinued, and the patient was treated with rituximab and high-dose methotrexate, resulting in stable disease. This case highlights that prolonged MMF therapy may confer sufficient immunosuppression to permit EBV-driven lymphoproliferative disease even in non-transplant patients. Early recognition, withdrawal of immunosuppression, and initiation of methotrexate-based chemotherapy can lead to favorable outcomes.